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GEOLOGY OF THE

ARABIAN PENINSULA

Yemen

GEOLOGICAL SURVEY PROPES IONAL PAPER 560-B

Geology of the

Arabian Peninsula

Yemen By F. GEUKENS

Translated from the French by s. D. BOWERS

GEOLOGICAL SURVEY PROFESSIONAL PAPER 560-B

A review of the geology of remen as shown on

USGS Miscellaneous Geologic Investigations

Map I-270A, "Geologic Map of the Arabian

Peninsula," I963

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON 1966

UNITED STATES DEPARTMENT OF THE INTERIOR

STEWART L. UDALL, Secretary

GEOLOGICAL SURVEY

William T. Pecora, Director

For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 - Price 30 cents (paper cover)

FOREWORD

This volume, "The Geology of the Arabian Pe1finsula," is a logical consequence of the geographic and geologic mapping project of the Arabian Peninsula, a cooperative venture between the IGngdom of Saudi Arabia and the Government of the United States. The Arabian­American Oil Co. and the U.S. Geological Survey did the fieldwork within the Kingdom of Saudi Arabia, and, with the approval of the governments of neighboring countries, a number of other oil companies contributed additional mapping to complete the coverage of the whole of the Arabian Peninsula. So far as we are aware, this is a unique experiment in geological cooperation among several governments, petroleum companies, and individuals.

'rhe plan for a cooperative mapping project was originally conceived in July 1953 by the late William E. Wrather, then Director of the U.S. Geological Survey, the late James Terry Duce, then Vice President of Aramco, and the late E. L. deGolyer. George Wadsworth, then U.S. Ambassador to Saudi Arabia, and Sheikh Abdullah Sulaiman, then lVlinister of Finance of the Government of Saudi Arabia, lent their support to the plan. InN ovember of the follow­ing year, 1954, Director Wrather approved the U.S. Geological Survey's participation and designated G. F. Brown responsible for the western Arabian shield region in which he had previously worked under U.S. foreign-aid programs. In January 1955 F. A. Davies, Chairman, Board of Directors, Arabian-American Oil Co., approved Aramco's participation and appointed the late R. A. Bra.mkamp, chief geologist, responsible for compilation of the area within the Kingdom where the sediments crop out. This responsibility fell to L. F. Ramirez following the death of R. A. Bramkamp in September 1958.

R. A. Bramkamp and G. F. Brown met in New York in February 1955 and planned the program, including scales of maps, areas of responsibility, types of terrain representation, and bilingual names. Thus there was established a cooperative agreement between the King­dom of Saudi Arabia, the U.S. Department of State, and the Arabian-American Oil Co. to make available the basic areal geology as mapped by Aramco and the U.S. Geological Survey.

The agreement specified publication of a series of 21 maps on a scale of 1:500,000, each map covering an area 3° of longitude and 4° of latitude. Separate geologic and geographic versions were to be printed for each of the quadrangles; both versions were to be bilingual-in Arabic and English. A peninsular geologic map on a scale of 1 :2,000,000 was to conclude the project.

High-altitude photography, on a scale of 1 :60,000, of the Kingdom of Saudi Arabia was initiated during 1949 by the Aero Service Corp. and completed in 1959. Both third-order vertical and horizontal control and shoran were utilized in compiling the photography. This controlled photography resulted in highly accurate geographic maps at the publication scale which then served as a base for the geologic overlay. The topography of the sedimentary areas was depicted by hachuring and that of the shield region by shaded relief utilizing the airbrush technique.

The first geographic quadrangle was published in July 1956 and the last in September 1962. While preparation of the geographic sheets was in progress, a need arose for early publication of a 1 :2,000,000-scale peninsular geographic map. Consequently, a preliminary edition was compiled and published in both English and Arabic in 1958. The second edition, containing additional photography and considerable new topographic and cultural data, was published in 1963. The first of the geologic map series was published in July 1956 and the final sheet in early 1964. The cooperative map project was completed in October 1963 with the publication of the 1 :2,000,000-scale "Geologic Map of the Arabian Peninsula" (Miscel­laneous Geologic Investigations Map I-270 A).

III

IV FOREWORD

As work on the quadrangles progressed, geologists, companies, and governments working in areas adjacent to the Kingdom of Saudi Arabia were consulted by Aramco and invited to participate in the mapping project. The number of cooperating participants was expanded to 11, which included the operating oil companies in the peninsula and which are identified elsewhere in this text; the Overseas Geological Surveys, London; the Government of Jordan; F. Geukens, who had worked in Yemen; and Z. R. Beydoun, who had studied the Eastern Aden Protectorate. ·with the close cooperation of the authors, the new data were added to data already plotted on· the base map of the Arabian Peninsula.

As the geological coverage of the peninsular map grew, the need for a text to accompany the map became apparent to both the U.S. Geological Survey and the Aramco geologists. Exploratory conversations were begun by Aramco with companies working in the other countries of the Arabian Peninsula for their participation in the preparation of a monograph on the geology of the Arabian Peninsula. Each author prepared a description of the geology of the area for which he was responsible, as shown in the sources of geologic compilation diagram on the peninsular· map. The U.S. Geological Survey undertook the publishing of the volume as a professional paper, ~nd the Government of Saudi Arabia was to finance its printing. It was early agreed that there would be no effort to confine the contributions to a standard format and that no attempt would be made to work out an overall correlation chart other than shown on the "Geologic Map of the Arabian Peninsula." Thus, the individual style of authors of several nationalities is preserved.

Cooperation and relations have been of the highest order in all phases of the work. The project would not have been possible without the full support of the U.S. Department of State, the Kingdom of Saudi Arabia, and all contributors. In fact, the funds which made publi­cation of this volume possible were contributed by the Saudi Arabian Government.

The data provided by the maps and in the professional paper provide information for an orderly scientific and economic development of a subcontinent. ·

~-t:1. b.:: Arabian-American Oil Co. (Retired).

,~r)~, w. D. STON, JR., u·

Former Chief, Foreign Geology Branch, U.S. Geological Survey.

CONTENTS

Foreword-----------------------------------------­Abstract-------------------------------------------Introduction _____ ------------_---------------------Physical geography ________________________________ _

Morphology ___________________________________ _ Meteorology __________________________________ _

General sketch of geologic history ____________________ _ Basement rocks _____________ --_------------ ______ - __ Sedimentary rocks _________________________________ _

Wnjid Sandstone _____ --- _________ --_--_-------_ Kohlnn Series ____ -_------ ____ -- __ --_--_---_---_ Amran Series ____ --_----------------------------

Type locality _____ --- _________ --_-- ___ - __ --_ Paleontology _____ --- ____________ -- ___ -_---_ LUhology _________________________________ _

South of Bftjil-f;lnn'a ____ .., _______________ _ Wadi Surdud and Wadi J_,a 'ah basins __ -- __ 'Amran-f;ln'dah-Al JawL _____________ -- __ Mn'rib-f;liifir ___________________________ _

Page

Ill

B1 1 2 2 2 3 5 6 6 6 8 8 9 9 9

11 11 12

Sedimentary rocks-Continued Tawilah Group ________________________________ _ Medj-zir Series ________________________ ... _______ _

Lithology _________________________________ _ Fossils and age ____________________________ _

Igneous rocks _____________________________________ _ Trap Series ___________________________________ _

Volcanic rocks _____________________________ _ Inter-Trap deposits ________________________ _ Age ______________________________________ _

Laccoliths ____________________________________ _

Geographic distribution _____________________ _ Age ______________________________________ _

Recent granites ___ - ____________________________ _ Recent volcanoes ______________________________ _

Structure _________________________________________ _ Gazetteer _________________________________________ _

Selected bibliography _______________________________ _

ILLUSTRATIONS

Page

B12 13 13 14 15 15 15 15 16 16 16 16 16 16 18 21 22

Pa~:c

FxounE 1. Block diagrnm and schematic north-south section __ :..----------------------------------------------------- B4 2-13. Photograph showing-

2. Basement and sedimentary formations exposed in the upper course of Wadi Surdiid______________ 5 3. Wajicl Sandstone outcrop·north of f;la'dah _________________________________________ -- _ _ _ _ _ _ _ _ 6 4. Wadi La'ah valley north of At Tawilah ____________________________________ ;.________________ 7

5. Granitic bnsement and overlying Wajid Sandstone in fault contact with Jurassic sandstone and lime-stone------------------------~-------------------------------------------------------- 8

6. Salt dome at f;lafir _________ ----------------------- __________________ --·-- _______ ------ _ ____ 12 7. Tawilah Group exposures at the town of At·Tawilah__________________________________________ 13 8. Medj-zir Series above Tawilah Group in the cliffs at Kawkaban__ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 14 9. Trap Series near Zarajah_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 15

10. Laccolith in the Kohlan Series in the upper course of Wadi Surdiid_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 16 11. Laccoliths in Al J a wf region __ · ____________________________________________________ ... _ _ _ _ _ _ _ _ 17

12. Recent granitic massif of Jabal f;labir and city of Ta 'izz at base of volcanic cone__________________ 17 13. Recent volcanoes ncar Rada' _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ .18

14. Profile of 'Amran graben_________________________________________________________________________ 19

15. Profile north of Ta'izz---------------------------------------------------------------------------- 20 16. Structure section in vicinity of Jabal Radman------------------------------------------------------- 20 17. Profile of Wadi Mahram ___________________________________________________ ·_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 21

TABLE

Pa~:e

TADI .. E 1. Fossils collected by F. Geukens------------------------------------------------------------------------- B10 v

GEOLOGY OF THE ARABIAN PENINSULA

YEMEN

By F. GEUKENS 1

English translation from the French by S. D. BowERS 2

ABSTRACT

After the leveling of tho Precambrian metamorphic basement toward the end of tho Paleozoic, sandy formations of continental facies were deposited mainly in the northern part of Yemen.

From tho Liassic onward a zone of subsidence occurred in the central and northern areas. This zone was filled with fluviolacustrine sediments. It was only from the Late Jurassic on that a marino transgression covered the entire territory. Tho zone of subsidence remains, more accentuated toward the Rod Sea.

During the Mesozoic, sandy conglomerates were deposited in tho areas of subsidence.

The last marino transgression, of Paleocene age, involved the central part of the country.

INTRODUCTION

The southwestern part of the Arabian Peninsula ' called "Arabia Fe1ix" in the ancient literature, was long

known as a mysterious and impenetrable country. Scientific exploration was limited to that done during a few journeys made by botanists, philologists, ento­Inologists, and others.

Geological studies did not begin in Yemen until the 20th century, but geographical exploration dates from the 18th century with the travels (dearly paid for by his companions) of Niebuhr in 1763, who succeeded in crossing the area between Allludaydah, $an'a, Ta'izz, and AI Mukha. Much geographical information was .acquired during the 19th century. The travels of Botta (1841) in 1836 and Passama in 1843, and the well documented journeys of archeologists Halevy from 1872 to 1879 and Glaser (1913) from 1885 to 1899 provided the foundation for future exploration.

1 Instltut GOologiquo do l'UnivorsitO de Louvain, Louvain, Belgiwn. 2 Arabian American Oil Co., Dhahran, Saudi Arabia.

The first regional topographic mapping was done by Beneyton (1913) for the purpose of constructing a rail­road and branch line from Allludaydah to $an'a. He mapped the borders of the triangular area between Ta'izz, $an'a, and Zabid (AI 1ludaydah). The first geological studies resulted from explorations by Botez (1912) along the Al1ludaydah-$an'a route during the Turkish occupation. Petrographic material which he brought back was studied by Roman (1925), who pre­pared an extensive report. Lamare (1923a) crossed the southwestern and central parts of Yemen, where he gathered considerable geographic and geologic data and established a preliminary stratigraphic column.

Some years later, Rathjens and Wissmann (1929) obtained permission to conduct scientific research in the AI 1ludaydah-$an'a-Ta'izz area. They made four trips-in 1927-28, 1931, 1934, and 1937-38-and completed the studies started by Lamare.

Werdecker's (1939) geographical work and Scott's (1939) descriptions of his scientific journeys furnish supplementary information concerning the area traveled by their predecessors.

Geologists Fricke (1953), Lipparini (1954), and Karrenberg (1956) visited the country for economic geological study. The purpose of their investigations being limited, they deviated only slightly from the tri­angular route from AI J;Ludaydah to $an'a to Ta'izz. Karrenberg was the first geologist to cover the Ta 'izz-Ibb-$an'a route by automobile.

In two journeys, 1953-54 and 1954-55, the author, as an expert under the technical assistance program of the United Nations, was able to travel through the country on a geological survey and visit previous]y unexplored regions, thanks to the cooperation of the United Nations Organization and the Government of Yemen (Geukens, 1960).

Bl

B2 GEOLOGY OF THE' ARABIAN PENINSULA

PHYSICAL GEOGRAPHY

MORPHOLOGY

Yemen can be divided into three physiographic provinces: a maritime plain called At Tihamah bordering· the Red Sea, a mountainous region drained by streams debouching into the Red Sea, and an interior undulating plateau in the east, between I,500 and 2,500 meters in elevation, where drainage flows inland.

The maritime plain, 30 to 40 kilometers wide, is a sediment-filled part of the Red Sea graben. It consists of two parts, the limits of which are not precise and are, therefore, difficult to trace. One part, adjacent to the Red Sea, is composed of late Tertiary and Quarternary marine formations covered by Recent eolian deposits. The other part, toward the interior, consists of thick deltaic deposits related to numerous in1portant wadis which disappear in the maritime plain. Numerous fresh-water springs are found near the border between the two parts.

The central mountain region occupies the west flank of a horst which lies between the Red Sea graben on the west and the Arabian desert on the east. The moun­tains are .dissected by wadis characterized by strong headward erosion which is highly diversified depending on the composition of the bedrock. South of Wadi La'ah, from Jabal Shu'ayb through Jabal ])awran and toward Ta'izz, the mountain region is incised by rivers (torrential during the rainy season) whose valleys progressively widen to the west. The many mountain massifs in this part are commonly secondary horsts. The terrain consists mostly of tuffs and compact lavas in horizontal attitude and explains the formation of steep ravines more than 1,500 to 2,000 m deep in several places. Near the outlets of the main wadis the valleys widen, and large stepped terraces alternate with moderately high hills. Near At Tihamah the western limit of the mountainous area is difficult to define because isolated hills emerge through the fluviatile deposits.

North of Wadi La'ah fluviatile erosion is more ad­vanced and has cut into basement rock and sedimentary formations. Thick calcareous strata form very steep cliffs, chiefly in the upper courses of these wadis Cllajjah and Kublan areas).

In the interior, plateaus of various dimensions range from I,500 to 2,500 min elevation and are covered with either fluviatile, eolian, or ·volcanic deposits. They are separated only by low hills. The southern part of the $an'a plain became a terrace by capture of the Wadi Wa'lan tributaries. In other places, the plateaus are cut by faults which form depressed areas and appear as alluvium-filled valleys-notably the plains of $an'a 'Amran, AI :l;Iarf, $a'dah, and others.

Generally, the interior plateaus grade without a sharp break into the more desert region to the east. This is illustrated in the northern part of the country where the Wadi al Jawf drops evenly to the desert. The area southeast of Jabal Mafluq is characterized by intrusive granitic n1ountains which rise above the calcareous plateau, and dense vegetation grows for smne distance along the main wadis. Local silt and loam plains are commonly formed through deposition behind ancient artificial dams. The true desert region begins east of the horst formed by Jabal Haylan and Jabal Balaq. The transition in this area from plateau to desert is locally very abrupt. The upper channels of Wadi Adhanah and Wadi Raghwan show very active head­ward erosion by the sharp intensification of relief east of Jabal ash Sharafah ('fiyal).

Contemporaneously with the subsidence of the Red Sea graben, young rivers brought large quantities of sediment. The subsurface of At Tihamah plain on the eastern side is formed of thick conglomeratic and other terrigenous deposits; on the western side, of salt, sand, shale and limestone.

At the end of the Pleistocene, tributaries to the Red Sea captured many tributaries of the rivers flowing toward the interior of the country. The capture as well as the decrease of rainfall during the Holocene explains the presence of gravelly fluviatile deposits standing out in relief in the desert region to the east, the surrounding sand having been removed by the wind.

METEOROLOGY

Precipitation in Yemen is strongly influenced by relief and consequently varies considerably from place to place. Meteorological observations were made by J. E. Hansen, engineer, and Dr. Carlo Toffolon, then personal physician to the Imam, at $an'a and Ta'izz from I942 to I944. According to their ob­servations at Ta'izz, the number of rains ranges from 90 to I60 per year, and annual precipitation ranges from 450 to 700 millimeters. Rainfall 1nay exceed 50 mm in a single torrential shower. Two rainy periods are distinguished at Ta'izz: (I) the most important pe~iod, in which precipitation may exceed 600 mm, extends from April to l\1ay, or in some years to June, and (2) a shorter period in which rain falls mostly during August and September. West winds predominate during the rainy seasons.

At $an' a annual precipitation ranges from 200 to 500 mm (60 to 90 showers) and also falls largely within two periods: (I) April to May and (2), the most important, from the latter part of July through the first half of August. Clouds generally gather on the west slopes of the main massifs and cause very heavy rainfall which accounts for the erosive action of the

YEMEN B3

wadis, the fertility of the land, and the. number of local springs.

GENERAL SKETCH OF GEOLOGIC HISTORY

Schistose formations cut by masses of Precambrian granite crop out 1nainly in the east, north, and north­west parts of the country as well as in son1e isolated horsts. Preliminary study of these areas did not lead to an adequate 1nappable subdivision.

The fornuttions have undergone regional meta­nlorphisin and intense folding in a general north-south direction. During this period important granitic 1nassifs were en1placed. Preca1nbrian formations ori­ented east to west were observed only in isolated places, a condition. which did not allow establishment of structurally differentiated units.

During a con tin en tal period of long duration, erosion converted the region to a Precambrian peneplain. Paleozoic transgression (Cambrian through Silurian?) probably extended over the area. Folding is indicated by a few remains of almost vertically inclined dark shales.

In another long continental period that followed, erosion almost cmnpletely removed the Paleozoic forma­tions and created a perfect peneplain on which a very leached almost entirely quartz soil developed. At the end of the Paleozoic, or Permian, the· peneplain was warped and the old surface was eroded in the south and redeposited as a delta or as dunes in the north (Wajid Sandstone). The beginning of the Mesozoic was characterized by a warn1 climate in which secondary basins forn1ed in northeast Yemen. These basins were filled by con tin en tal red sandstones, indicating the nearness and influence of the landmass. Deposition of dark-green and gray-black shales of fluviolacustrine origin (ICohlan Series) followed. In isolated bays or near the coast short periods of emergence resulted in the forn1ation of gypsum lenses.

During the lVfaln1, the most important transgression extended over the entire country, and formed shallow­water calcareous deposits (Amran Series). Initially, the transgression followed along local depressions. An example of such a depression is northwest of $an'a where Bathonian to Callovian carbonate rests on the Kohlan Series. To the north where the limestone is 1nore chalky, the transgression was a little later (Callovian to Oxfordian). This area corresponded to the neritic zone containing stromatoporoids, and was separated fron1 the great basin which extends into Saudi Arabia.

Commencing with the Oxfordian, the transgression covered the whole eastern and southern parts of the country. During this period subsidence zones formed in the desert area of Ramlat as Sab'atayn and in south-

21!)-251 0-GG--2

west Yemen. In the central and southern parts of the country, Late Jurassic marine transgression took place directly on the Precambrian basement. (See fig. 1.)

A period of continental environment followed to­ward the end of the Late Jurassic. A lagoonal stage occurred in the center of the depressions, where gypsum and salt were deposited, while the margins of the basins emerged and were subjected to erosion. Con­tinental sandy conglomerates of Cretaceous age (Ta­wilah Group) were laid down, probably over the entire area. The Tawilah Group is found wherever it is covered and protected by the overlying Trap Series. Tilting followed, along with greater deposition of sand in the flat-bottomed basins.

During the Paleocene a narrow sea spread over the center of the country; the neritic facies (Medj-zir Series) attests to the nearness of the landmass, where a tropical climate formed lateritic soil on its exposed surface.

Tectonic movements, resulting in faulted domes, affected especially the central part of the country, where Jurassic and Cretaceous beds were removed by erosion at the beginning of the Tertiary.

· Intense volcanic and intrusive activity began locally at the end of the Cretaceous and became widespread during most of the Tertiary. Volcanism is especially evident in southwestern Yemen where flows and tuffs locally exceed 1,500 m thickness (Trap Series); silicic laccolith intrusions are more common to the north. Calm intervals during the Oligocene and Miocene produced fluviolacustrine deposits interca]ated with the Trap Series. Very intense tectonic activity char­acterized by normal faulting continued to the end of the Tertiary. Recent granitic intrusions penetrate the Trap Series, especially in the western part.

In the Quaternary, volcanic materials were sporadi­cally distributed over the whole country; large areas of basalt flows and many craters characterize the central part of Yemen near $an'a, Dhamar, and l\1n'rib. Small basnltic craters are irregularly dis­tributed over the entire territory.

l\1njor loess deposits extend widely over the p]nteaus. Recent faults which facilitated erosion abruptly limit the areal extent of the loess fields.

Structural deformntion has strongly 1nodified the drainage pn,ttern. Examples of very recent strenm cnpture and indications of future capture nre noted in the terrain, especially south of l\1nJ).wad. l\1ajor terraces occur not only in the lower chnnnels of the wadis but also in the upper channels of the Red Sea tributaries where the waters erode the old fluviatile deposits related to the wadis which flow eastwnrd toward the interior of the country.

'S<" I',. ,...""""'---~ (

'S<""G\y( ~- ·· .. \, ,; ., " ,;

""<--1 'o<S<' "" s~ ,; ("'

EXPLANA

~ Laccoliths (Tertiary)

D < _,

Trap Series (Upper Cretaceous and Tertiary)

ITd Medj-zir Series (Paleocene)

~ Tawilah Group (Cr~taceous)

~ -Amran Series (Upper Jurassic) Wajid Sandstone (Permian or older)

"'~~ '< • ''r ',• .'_,.·I

Kohl an Series (Liassic) Basement complex (Precambrian)

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METERS '400

hoo

~~

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) ,J

( ' ("

~ .,~ - ..... ....__c,

FIGURE 1.-Block diagram showing sedimentary units in Yemen and a schematic north-south section.

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0 ~

.....,

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~ '"d t_%j

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YEMEN B5

BASEMENT ROCKS

A complex, not yet subdivided, underlies all the subhorizontal sedimenta:ry formations. It is composed of highly metamorphosed rocks enclosing large granitic massifs. The basement crops out mainly in the eastern and northern parts of Yemen, as well as in the bottoms of horsts which are uplifted through the Trap Series.

In the eastern part of the area of horsts north of Ta'izz, the basement consists mainly of mica schist (oriented generally north to south) and pink granite which has two micas and contains pegmatite and aplite veins. In the central part the granites contain large gneiss and mica-schist xenoliths, at places measuring several tens of meters in thickness .

The basement in the horst south of Bajil is likewise composed of gneiss and J;Uica schist, as well as pink orthoclase granites.

The basement exposed south of Wadi Surdud is com­posed of mica schists oriented east to west and dipping 45 °S. In the Wadi Surdiid (fig. 2) farther north, granite exposures include large mica-schist xenoliths.

In the floor of Wadi La'ah north of At 'fawilah, the Precambrian is oriented N. 40° W. and dip is nearly vertical. It consists of chlorite schist, garnet schist, and gneissic quartzite. Several pegmatite veins, 20 to 50 centimeters thick, containing black tourmaline

crystals as much as 14 em long, cut the basement. Downstream, the metamorphic series includes three granite massifs.

The anticline uplifted between Rada' and $irwab. in the southern part near the Aden Protectorate frontier is a highly folded complex oriented generally N. 10 ° E. The folds show very pronounced dip.

Farther north, in the upper channel of Wadi Adhanah, the basement is composed of gneiss, mica schist, and amphibolite. Nearly midway between A<;l l)ayq and $irwab., the basement includes a conglomerate layer which appears to separate two different tectonic complexes.

In the $irwab. area the general orientation of the Precambrian is north to south. West of the town, gneiss and garnet schist crop out; to the east, gneiss and mica schist are exposed.

Toward Ma'rib, west of Jabal Balaq, mica schist, quartzite, a_nd amphibolite (oriented north to south) are exposed. This great Precambrian dome plunges to the north near the upper channel of Wadi Raghwan.

Jabal Dakhan, 25 kilometers northwest of $irwab., is a granite dome more than 5 km long. On the east and west slopes, the granite is covered by a thin q\lartz­itic bed overlain by green chlorite schist which grades into gneiss and amphibolite within several meters

FIGURE 2.-Basement and sedimentary formations exposed in the up er course of Wadi Surdiid. F indicates fault.

B6 GEOLOGY OF THE· ARABIAN PENINSULA

East of Jabal 'fiyal, the basement consists of gneiss and garnet schist overlain by quartzite.

The Precambrian basement is exposed for a long distance in the horsts marking the limits of the two sides of the $a'dah graben. The east horst is pink granite near $a'dah, and gneiss and mica schist farther north. North of Wadi Akwam the basement includes white marble much deformed by tectonic movements. The marble is locally mineralized by ilmenite at the contact with gabbro intrusives. Farther north of Wadi Akwam (tributary of Wadi Najran) , the white marble crops out as lenses appearing as small white hillocks surrounded by fluviatile deposits.

Toward the Saudi Arabian frontier, the basement is composed of grayish-black mica schist and gneiss oriented north to south and includes some granitic massifs.

The west $a'dah horst consists, from south to north, of mica schist, granite and pegmatite, biotite schist, and quartzite locally containing magnetite.

Compared lithologically with the Precambrian of Saudi Arabia, the basement would be the equivalent of the oldest formations grouped in the Hali Schist.

SEDIMENTARY ROCKS

WAJID SANDSTONE

A well-stratified sandy conglomeratic formation covers the Precambrian basement for a great distance east and north of the Jawf area and north of $a'dah

(fig. 3). The southern boundary east of Al Jawf is a fault . Some remnant hills (Jabal an Nu'aym) still exist in small isolated grabens west of the $a'dah depression. 1

This IOrmation is composed mainly of well-rounded white quartz sandstone and conglomeratic gravel lenses. In Jabal Dalhan, north of $a'dah, it exceeds 200m in thickness. Apparently, the Wajid Sandstone repre­sents deltaic deposition by rivers flowing from the southeast. Toward Wadi Najran, the sandstone forms a thin cover over the plateau, a cover partly removed by the wadis and their tributaries . To the north, the Wajid Sandstone is less coarse grained, possibly formed, in part, of eolian deposits.

The stratigraphic contact between the Wajid Sand­stone and the Kohlan Series was not observed because a fault separates the Wajid and Kohlan where they approach each other. Sedimentary conditions for these two sequences are quite different. The per­centage of quartz is very high in the Wajid and greatly exceeds that of the Kohlan. Owing to the complete lack of index fossils in Yemen, we must look for the stratigraphic evidence in Saudi Arabia. Near the frontier the Wajid Sandstone is mapped as being of Permian age or older (Brown and Jackson, 1959).

KOHLAN SERIES

Below the Upper Jurassic Amran Series in Jaba Muf;>awwar, Lamare and Carpentier (1932) found sedi

FIGURE 3.-Wajid Sandstone outcrop north of $a 'dah.

(

YEMEN B7

mentary rocks which they were able to date as Liassic from plant fossils found in the upper part. The beds were grouped by this author in the Kohlan Series, which is exposed mainly in the central and northern parts of Yemen. To the north the Kohlan Series does not go beyond the latitude of $a'dah, and to the northeast it is· bounded by the mr.jor horst which extends from $a'dah-Jabal Barat to Jabal al Lawdh. The southern extension includes a pre-Trap Series horst which bounds the At 'fawi:lah-$an'a Jurassic basin on the south (upper course of Wadi Surdud). The series shows great facies variation from south to north and from east to west.

The series is highly arenaceous southward in the upper channels of Wadi Khawbah and Wadi al 'Urr, west of Jabal Shu'ayb, the highest mountain in Yemen . Resting on the basement and directly overlain by the Trap Series, the Kohlan in this area consists of yellow­ish-white sandstone with conglomerate lenses containing well-rounded quartz fragments. It is better exposed and thicker a little farther north in Wadi Nasim (upper course of Wadi Surdud). Here, the gneiss basement is overlain by about 150m of white sandstone interbedded with many layers of conglo~erate, violet fine-grained sandstone, and white crossbedded coarse-grained sand­stone containing pseudonodules. There are also several zones of irregular accumulations of hematite. One hundred meters from the base, beds containing green­white, green, and red chert nodules are interbedded with conglomerate containing quartz fragments and green­gray shale debris. These are fluviolacustrine and neritic formations, and are probably equivalent to the green shale beds which crop out on the south side of Wadi La'ah where Lamare found a Jurassic flora. The neritic facies thins toward the north. The conglom­erate beds, numerous north of Wadi al 'Urr, are almost completely absent in Wadi Surdud, whereas shaly and tuffaceous beds are present to the north.

Section of Kohlan Series on south side of fit J'awilah

(sec fig .4) Amran Series at top of section .

Kohlan Series:

of Wadi La'ah, north

Thickness (meters)

Sandstone and shale; violet-red sandstone, and slaty shale overlain by gray. shale______________________ 50

Shale, sandstone, and gray shale overlain by conglom-eratic sandstone and 3 m of red shale ___ .__________ 18

Shale, gray-green; includes large rounded blocks of granite, pegmatite, and gneissic mica schist as much as 1 m in diameter_ _____________________________ 7

Shale and conglomerate, a few meters of basal con­glomerate containing basement fragments; some very thin conglomeratic layers with very fine well­stratified fragments, overlain by slightly green-gray shale_______________________________ ___________ 25

Total ______________________ __________________ 100

Basement at base of section.

FIGURE 4.-Wadi La'ah valley north of fit J'awilah.

The upper calcareous gray shale contains the Amran Series fatma; thus the boundary between the Kohlan Series and the Amran Series is arbitrary because there was no break in sedimentation. From this section, it appears that the zone of large blocks about 7 meters thick separates an older complex about 25 m thick. Lamare without specifically stating so in his text, like­wise depicted a conglomeratic bed with large fragments in his stratigraphic section.

The Kohlan Series may actually include two complexes of different age-the lower being more shaly. In any case, the sandstone facies thickens toward the west; in the lower course of Wadi La'ah, the Kohlan Series is several hundred meters thick (700 m according to 0. Schmidt, oral commun., of C. Deilmann Bergbau). North of Jabal Mu:;;awwar, the series is about 300 m thick (Lamare, 1930b, and Wissmann and others, 1942). Thicknesses given by different authors do not compare closely because the upper boundary of the Kohlan Series is difficult to determine.

A complete section of the Kohlan Series is not exposed in any part of the Stt'dah area. Nevertheless, a part of this series about 125 m thick is exposed north of As Sinnarah (Jabal 'A blah), the mountain on which the

B8 GEOIJOGY OF THE ARABIAN PEN·INSULA

fortress of Sa, 'dah is constructed (fig. 5). From obser­vations made west and southwest of Se,'dah, it seems probable that a complete Kohlan section is exposed at Jabal 'Ablah.

Section of Kohlan Series at Jabal 'Ablah, north of As Sinnt:irah

Amran Series at top of section.

Kohlan Series : Thickness

(meters)

Sandstone, gray, hard, with worm tracks. Progressive transition to the overlying Amran Series___ ________ 15

Sandstone, white, crossbedded___ ___________________ 10 Sandstone, white, friable, crossbedded; red sand with

ripple marks___ ______________________________ __ 26 Sandstone, calcareous and vuggy____________________ 14 Sandstone, gray, light-gray to yellow, friable_ ________ 10 Sandstone, coarse-grained, red and yellow, crossbedded,

and white poorly cemented sandstone_ _ _ _ _ _ _ _ _ _ _ _ _ 18 Shale, pebbly; conglomeratic layers with gray shaly

cement and fragments as much as 10 em in diameter_ 20 Clay shale, light-gray_____ _________________________ 2 Sandstone, coarse-grained, with a red crossbedded band

and irregularly disseminated pebbles and gravelly layers__ ________ _____ _________ _________________ 8

Conglomerate, coarse; fragments as large as 10 em in diameter; contains pebbles of volcanic rocks___ _____ 2

Total __________________________________________ 125

Basement at base of section.

These observations show that at the time of Kohlan deposition a zone of subsidence, which is now more

pronounced toward the Red Sea, existed m central Yemen.

AMRAN SERIES

TYPE LOCALITY

The calcareous formations which crop out over a large part of Yemen, especially in the north, were grouped by Lamare in the Amran Series. 'Amran, a town about 40 km from $an'a, is in the bottom of a northeast-trending secondary graben. It has not been possible to locate precisely where Lamare established the type section, but he does show a figure in which he defines the Amran Series (Lamare, 1930b, p. 52).

The fossils of Jurassic age found in the lower part of the Tawilah Group, as defined by Lamare (beds 13 and 14), permit modification of the type section and the proposal of the outcrop in the south side of Wadi La'ah as type locality of the Amran Series. All the sedimentary sequences of Yemen except the Wajid Sandstone are exposed in this valley.

The Amran Series crops out mainly in the $a'dah­Jabal Mu~awwar-Ma'rib area, although it formerly covered the entire country. In fact, traces of Amran rocks are found in the extreme eastern sector of the country, notably in the desert area of $afir, in the far south near the frontier along Wadi Bana, as well as in the west in an isolated horst which is uplifted through the Trap Series. The facies varies from place to place but is everywhere calcareous, a characteristic whicb

FIGURE 5.-Granitic basement and overlying Wajid Sandstone in fault contact with Jurassic sandstone and limestone. Walls of S~'dah in the foreground.

YEMEN B9

easily distinguishes this series from the upper sand­stones and fron1 the lower shales and sandstones.

In the type area, Laillare (1930b) estimated the series to be 320 111 thick; however, the thickness is highly variable from place to place in relation to local subsi­dence. Since the first exploration, the Amran Series has produced fossils which establish its age as a Maln1 eq ui valent.

PAI.JEONTOLOGY

Fossils collected by Botez (1912) in the Bajil area: Cidaris cenornanensis Cotteau Exogyra africana Lamarck Ostrea syphax Coquand Ostrea ouremensis Choffat Ostrea dieneri Blanckenhorn Nerinea sp. Natica sp. Terebratula sp. Rhynchonella sp.

Fossils collected by Lamare (1930b) in the 'Amran-Kublan area: Cidaris alandarius Lang Rhynchonella rnoravica Uhlig Terebratula sttbsella Leymerie Avicula cf. A. gessneri Thurmann and Etallon Ostrea suborbicularis Roemer Ostrea thurmanni Etallon Alectryonia pulligera Goldfuss Exogyra bruntrutana Thurmann Modiola subangustissima Dacqu6 J1,1ytilus sttbpectinatus d'Orbigny Area sublata d'Orbigny I socardia ( = Ceromya) striata d' Orbigny Lttcina sttbstriata Roemer Cardium banneanum Etallon Pholadomya protei (Brongniart) Anatina ( = Cercomya) striata d'Orbigny Anatina ( = Cercornya) sp. indet. Natica hemisphaerica Roemer Natica sp. Tylostoma sp. indet. Perisphinctes cf. P. virguloides Waagen Perisphinctes aff. P. praestenococyhts Waagen Perisphinctes ( Virgatites) cf. P. dorsoplanus (Vishchniakoff

Burckhardt

l!"'ossils collected by Herbert Karrenberg (in Basse and others' 1954) north of f;ian'ii.:

Modioltts (Pharomytiltts) cf. M. perplicatus Etallon Exogyra nana (J. Sowerby) Exogyra sp. inclet. Lopha karrenbergi Basse Gryphaea balli (Stefanini) Praeconia rhomboidalis (Phillips) Protocardia somaliensis Cox Cardium sp. Pholaclom.ya (Homomya) inornata J. de C. Sowerby Nerinella retrogressa Etallon Nerinea acreon d'Orbigny N erinea binodosa Etallon Cryptoplocus subpyramidalis Munster Cryptoploctts n. sp. Basse Cryptoplocus yemenensis Basse

Globularia hemisphaerica Roemer Spinigera sp. inclet. Pseudocidaris thurmanni Etallon Terebratula subsella Leymerie Comophyllia thamnastroides Gregory Plesiophyllum harensis Basse

Fossils collected by Geukens are listed in table 1.

LITHOLOGY

The Amran Series may be differentiated by facies in four areas, as follows: (1) South of Bajil-$an'a; (2) Wadi Surdud and Wadi La'ah basins; (3) 'Amran-$a'dah-Al Jawf, and (4) Ma'rib-$afir.

SOUTH OF BAliL-~AN' A

South of the Bajil-$an'a area the Amran Series is exposed in small horsts uplifted through the Trap Series. In the northern part of this area, the series begins with a 1- to 2-Ill thick basal conglomerate that contains basement fragments 2 to 3 em in diameter. Above this are beds of blue-gray iimestone with luma­chelles. This unit is overlain by the dark-gray lime­stone which is predominant througho~1t the whole series. The thickness of the series does not exceed 250 Ill.

In the southern part of this area, the top of the An1ran Series is marked by 2 to 3 Ill of dark-gray shale and calcareous shale characterized in the upper part by signs of emergence and slightly violet shale and lime­stone.

Toward the west, the Amran Series limestones are dark blue and contain l\1ytilidae and Ostrea which were transported· a great distance. Near the longitude of Ta'izz, the base of the series rests on. the Precambrian and is con1posed of a few meters of piBk quartzite and conglomerate containing sn1all fragments overlain by thick beds of dark-blue limestone. A- -shaly cmnplex about 200 m thick overlies the blue~g·mtY lin1estone extending westward toward At Tihanl~lltlo1~ This conl­plex of green and violet shale with gyp~~~hl lenses is overlain by 100 n1 of dark shale, includin~J.)5~ds of gray lin1estone, in turn overlain by calcareous's~bdstone (30 111 thick) and a shaly complex with several thin lenses of Inarl and limestone. The contact with the Tawilah Group is very distinct.

To the south, the Aniran Series consists of thick beds of dark-blue limestone, thinning to the east, which were deposited on the basement as a result of a marine transgression fron1 the west. Many lumachelle beds show that the subsidence was slight and that the basin was progressively filled. After a period of emergence, a lacustrine period followed which was succeeded, in turn, by slight subsidence during which Upper Jurassic

. limy-marly and shaly deposits were laid down.

BlO GEO:UOGY OF THE ARABIAN PENINSULA

TABLE I.-Fossils collected by F. Geukens

~ "' .s:: Ci3

Q "' ~

~ r.::l "C) Ci3 "" "C) "C) .s:: .s:: a ~ .s:: "C)

s -~ .s:: "' "' "' "' .0 •:::l .... ,1d ~ :0 :a E-to ~ '"Cio C'

"C) "' .0

~ "' "' Q idl "" -< ..c::lo ...., !::;. ::; Q ~ "' "' :>-. ...

.0 ~ ~ t:: ·~ -= Q Ci3 < ~ :>-. "' C/}t

.0 rJ.l '§ 0 ~ Ci3 ~ :a :g "' 00 Ci3 "' ~ 0 ·.: :a C/}t .0 0 0 ~ "' r:.r:l .s:: .0 '"' .s:: .0 "' '"Cio t::

...., '"' .s::

z ~ o:l < t:: ~ < -< "' ~ z r:.r:l < -< ~ t:: ~ ..., ...., rJ.l

-------------------1---1----------------------------------

Bourguetia striata J. Sowerby __________________ .... ., .. ________________ X ____ ---- ____ ---- ____ ---- ---- ---- ---- ----Burmirhynchia? ____ ------------------ ____________________________________ X ____ ---- ____ ---- ---- ---- ---- ----Camptonectes aff. C. virdunensis

(Buvignier) ________________________ - _- ___ - - .. ___________ - _________ - X ---- ___ - ---- _--- ---- ---- ---- ---- - .. --Ceratomya cf. C. plicata Agassiz ________________ ---- ____________ X ________ ---- ____ ---- X ---- ---- -------- ----Ceratomya cf. C. wimmisensis ( Gillieron) .. __ .. _____ .. - _ .. ______ .. __ - _ .. _ _ _ _ X .. _-- .. - .. - ___ - -- _- _--- ---- ---- .. --- ---- .. ---Ceratomyopsis cf. C. kiliani (Roilier) ___________ ---- ________________ X X ---- ____ ----------------------------Chlamys (Chlamys) c·u~vivarians

Dietrich __________________________________ ---- ________ ---- ____ X ____ ---- ____ ---- ---- ---- ---- ---- ---- ----Chlamys sp __________________________ ---- X ---- ____ ---- ---- ____ ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ----Daghanirhynchia? _____________ .. __ ...... __ .. _- _ .. -- -- .. _ .. ______ .... - ___________ --- X .. __ - --- .. ---- ---- ---- - .... - ---- - .... -Eligmus cf. E. aualites (Stefanini) ______________ ---- ________ ---- ____ X ____ ---- ____ ---- ---- ---- ---- ---- ---- ----Exogyra _____________ ·-!---:,----.-:------ ________ ---- ____ -------- ________ -------- ____ ---- X --------------------Eligmus cf. E. rollandi Douville ________________ ---- ____ -------- ________ X ---- ____ ---------------- ------------Exogyra nana (J. Sowerby) ____________ X X ---- ____ ---- ---- ____ ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ----Exogyra Fourtaui StefaninL ___________________ ---- ____ ---- ---- ________ X ---- ____ ---- ---- ---- ---- ---- ---- ----Hem icidaris ( H ypod iadema) M acf ad yem·

(Currie) __________________________ ------------ _____ · ___ ---- ____________ ---- ____ ---- ____ ---------------- X Globularia sp _________ .. _______ -- __ .. -- ---- X -- ______ - .. _- -- _________ - _ --- ---- ___ - -- ___ - _- -- __ - -- - ---- - - - - X Homomya inornata (J. de C. Sowerby) __________ ---- ____________________ X ____________________________ ---- ----

Inoperna perplicata (Etallon) __________ ---- ---- ---- ---- ---- ---- ____ X -------- ---- ---- ---- ---- ---- ---- ---- ----Lima (Plagiostoma) SP---------------- ___ ·_ X -------------------- X ---- -~-- --------------------------------Lima (Plagiostoma) harronis Dacque ____ ---- ---- ---- ---- ---- ---- ____ ---- ---- X X ---- ---- ---- ---- ---- ---- ----Lopha solitaria (J. Sowerby) ___________ ---- ---- ---- ____ ---- ---- ____ X X ---- ---- ---- ---- ---- ---- ---- ---- ----Mactromya SP----------------------- ------------------------ ____ X ---------------------------- ------------M actromya aequalis Agassiz __ ---- __ --- ---- ---- -- _- ____ ---- ---- _--- ---- X ---- ---- ---- ---- ---- ---- ---- ---- ----Modiolus imbricatus J. Sowerby ________ ---- ---- ---- ____ ---- ---- ____ ---- ---- ---- ---- ---- ---- X ---- ---- ---- ----Modiolus jurensis (Roemer) ___________ ------------ X ---- ---- X ---- ---- ---- ---- ---- ---- X ---- ---- ---- X Brachidontes (Arcomytihts) laitmairensis

(de Loriol)-----fp----------------- ------------ ____ -------- ____ X -------------------- X ----------------N erinea X X X - - - - X - - - - - - - -

~~;::do~;~::::::~:::::::::::::::::: :::: :::: : ~: : ~: : ~: :::: :::: :::: :::: :::: :::: :::: :::: -~- :::: :::: -~- :::: Pholadomya aulMIJi Douville ______________ ·_------------------------------------------------ X ---- ---- ---- ----Pinna cf. P. stottczkai Cox ____________ -------------------------------- X ---- ---- ---- ---- ---- ---- ---- ---- ---Pseudocidari~rJ~'flrmanni Etallon _______ ---- X ________________________________________ ---- ---- ---- ---- ---- ----

~~::~~~~~:~t4:~:j;i-c~~;w~ir--~~~~~~~~~ ~~~~ ~~~~ ~~~~ ~~~~ ~~~~ -x- ~~~~ ~~~~ -~- ~~~~ ~~~~ ~~~~ ~~~~ ~~~~ ~~~~ ~~~~ -~- ~~~~ Somalirhynchia ~africana var. mesoloba

l\1uir-Wood _______________________ ---- ---- ---- ---- ---- ---- ---- ---- X ---- ---- ---- ---- ---- ---- ---- ---- ----Terebratula cf. T. bicanaliculata

Schlotheim ________________________ ---------------------------------------- X Terebratttla aualites Stefanini_ _________ ---------------------------- ------------ X ---------------- ---- ---- __ .... Terebratula SP----------------------- ---- X X ---- ---- X ____ X ---- ---- ---- X ---- ---- X ---- ---- X Terebratula sttprajurensis (Thurmann)-- -- .. - -- .. - -- .. - ...... - ---- .. - ~- -- .. - ---- X ---- ---- ---- ---- X ---- ---- ---- ----Trochalia cf. T. yemenensis (Basse) _____ -------- X ---- ---- ---- ---- ---- ---- ---- ---- X ---- ---- ---- ---- ---- ----Trochalia depressa (Voltz) _____________ -------- X ---------------------------------------------------- --------corals ______________ .. _____ .. - ...... -_--- ---- ---- ---- ---- ---- X -- .. - - .. -- X ---- ---- ---- ---- ---- ---- ---- ---- ----echinoids ___________________________ -------------------- X ---------------- X ----------------------------gastropods __________________________ ---------·--- X -------- ---------------- X -------- X ----------------pelecypods _____________ .... -_---- .. _--- ---- ---- ---- X ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ----plant debris _________________________ ---------------- X X ---- -------- X ---- ---- ---- ---- ---- ---- ---- ---stromatopores _______________________ ------------ ____ ---- X ________ X -------------------- X ------------

YEMEN Bll

WADiSURDUD AND WADi LA'AH BASINS

In the Wadi Surdud-Wadi La'ah basins, the upper and lower boundaries of the Anuan Series are more difficult to determine. This is natural considering that in this area subsidence began before deposition of the Amran Series and continued into later epochs. For exan1ple, on the north side of the Wadi Surdud valley near the junction with Wadi al Ahjar, the lower sandstone series (Kohlan Series) grades progressively upward into limy and Inarly beds of the Amran. In that area the series, at least 360 m thick, consists of about 300 m of pure limestone and shaly limestone. 'fhese calcareous rocks are overlain by light-green and light-yellow shale and some sandy beds that enclose alternating layers of black shale and marl. This sequence grades progressively upward into sandy con­glOineratic beds of the Tawilah Group.

In the upper channel of Wadi al Ahjar, the shaly­rrmrly part of the Amran becOines more continental, whereas the limestone becomes more marly.

Section of Amran Series in 1tpper channel of Wadi al Ahjar Conglomeratic sandstone of Tawilah Group at top of section.

Thickness Amran Series: (meters)

Sandstone and violet shale _________________ -_---_-- 20 Sandstone, ribboned; includes plant remains and a few

beds of nodular sandstone________________________ 20 Shale, violet and green _______________ -- ___ -_-_---- 15

Total__________________________________________ 55

Typical limestone and marl below. In this upper part of the Amran Series, beds of

gypsum and dark bituminous shale increase toward the east, as seen in the east side of Wadi al Ahjar, and have been recognized north of $an' a in wells drilled in 1953 by German engineers to study the bituminous shale.

In spite of the gradual transition to adjacent series, the 1nost con1plete section and the easiest to study is in the south side of Wadi La'ah.

Section of Amran Series in south side of Wadi La'ah Tawilah Group at top of section.

Thickness Amran Series: (meters)

Limestone and shale: shaly limestone, interbedded gray shale, and a few limestone beds containing many large sea urchins are overlain by alternating marly limestone and light-yellow argillaceous shale, many spicules, and Lima (Plagiostoma) harronis Dacqu6 ________________________________________ 140

Limestone, thick-bedded; large Ostrea ___ - _---------- 50 Limestone and shale: complex of thick beds of light­

gray limestone separated by shale lenses; toward the top the limestone beco.mes more marly and yellow- - 170

Shale, calcareous, gray; Terebratula cf. T. bicanaliculata Schlotheim and T. aualites StefaninL ______ -------- 20

Total __________________________________________ 380

Kohlan Series at base of section.

The Amran Series thus consists of 380 m of pre­dominantly light-gray limestone, the upper part of which contains a shaly~marly-limy complex 90 m thick. This thick sequence occurs, however, in the axis of subsidence; toward the north and west the Amran Series is not as thick.

Just south of Ath Thillah, the top of the calcareous Jurassic rock is in direct contact with crossbedded gravelly and sandy beds; at the contact is a conglom­eratic breccia having calcareous cement. This is the margin of the Jurassic basin which emerged prior to the Cretaceous. ·

Toward the west in the direction of Mahwad, the upper part of the light-gray limestone containing Trochalia yemenensis is overlain by about 20 m of sandstone interbedded with generally violet shale and limestone overlain by red sandstone. The sharp thinning of the marly-limy beds seen at At Tawilah, the arenaceous facies, and the violet coloring show that the Mahwad area represents the western margin of the Late Jurassic basin.

The Jurassic reappears farther to the east on the west flank of a large anticline with a Precambrian core, where a sharp thinning of the Amran Series is also observed. The upper marly-limy part seems to be completely eroded here, and the base of the sandstone of the Tawilah is composed of conglomerate with limestone fragments.

'AMRAN-~A'DAH-AL JAWF

In the 'Amran-$a 'dah-Al Jawf area only rocks of the Amran Series crop out. Bounded on the northeast by faults and on the west by unexplored ravines, the area is not favorable for paleogeographical study. The region is characterized by predominantly light­yellow marly limestone, reminiscent of the upper part of the Amran Series in the Wadi La'ah valley. That these are shallow-water deposits is indicated by (1) many intercalated sandy layers and interstratified gypsum lenses, as for example, at AI !Iarf southwest of $a'dah, (2) claystone lenses and crossbedded sands with plant debris alternating with calcareous beds containing globular stromatoporoids and isolated corals, (3) beds filled with Cidaridae spicules, (4) beds showing traces of emergence and crossbedded sandy limestone.

The stratigraphy of the top and bottom of the series is more complex. Toward the base the Amran Series passes without interruption into the Kohlan, as demon­strated in the section near Jabal 'A blah southeast of $a 'dah.

The upper part is exposed in the synclinal axis in the 'Amasiyah area and consists of a dark-yellow to buff sandy layer containing plant debris.

B12 GEOLOGY OF THE ARABIAN P ENI NSULA

MA'RIB-SAFIR

The Amran Series is exposed in the desert region of Ma'rib-~afir, but rare outcrops only give a general idea of the evolution of this part of Yemen.

The base of the series rests on the metamorphic base­ment exposed on the southwest side of Jabal Balaq, west of Ma'rib. The basal part consists of 1 to 2m of coarse-grained quartzite overlain by oolitic limestone and calcareous and sandy shale. The series itself is composed of light-yellow marly limestone similar to that at ~a'dah, but containing, on the east side of the jabal, many beds of alabaster and white marble which were quarried in ancient time. Eastward near ~afir ,

the Amran Series consists of major salt deposits over­lain by bituminous shales, several meters of gypsum, and yellow-gray argillaceous and calcareous shale con­taining fish remains (fig. 6). The character of the rocks in the upper part of the Amran Series indicates a major isolated basin characterized by desiccating conditions .

TAWILAH GROUP

The Tawilah Group is composed mainly of white coarse-grained sandstone containing at irregular inter­vals conglomeratic layers of rounded or subangular quartz fragments; red sandstone is intercalated locally.

In the upper par t, generally immediately below the Trap Series, are beds containing globules or nodules of hematite . To date, no fossils have been collected from this group , which is considered to be of Cretaceous age by reason of geometric relationships.

Type section of the Tawi/ah Group at J abal at 'fawilah (sec fig. 7)

Medj-zir Series at top of section. Thickness

Tawilah Group: (meters)

Sandstone, white, crossbedded; coarse conglomerate lenses _________________________________________ 120

Sandstone and shale; violet shale in thin beds inter­stratified in white sandstone_ __ ___________________ 20

Sandstone and shale; white sandstone with conglom­erate layers alternating with red and green shale____ 40

Total ____ _________________________ _____________ 180

Arman Series at base of section.

The delineation of the upper boundary is rather arbitrary in the zones of subsidence, such as in the zone west-northwest of ~an'a, although breaks in sedimentation occur elsewhere which allow more precise determinations of the boundaries of the group.

Because coarse-grained sandstones and gravelly layers everywhere characterize the Tawilah Group, the shaly-sandy transition beds (55 m thick) containing

-... - -·

,

-..

FIGURE 6.- Salt dome at ~afir.

YEMEN B13

FIGURE 7.-Tawilah Group exposures at the town of A~ Tawilah.

plants were considered Jurassic. These beds crop out in the upper channel of Wadi al Ahjar above Jurassic limestone .

The group is less thick (150 to 200 m) in the area north of Ta'izz where it may be studied in isolated horsts . At the base is a gray brecciated bed, about 1 meter thick, containing limestone fragments and is overlain by numerous conglomerate beds interstratified in coarse-grained sandstone.

The upper part includes white sandstone with layers of iiTegular hematite nodules, crossbedded sandstone, conglomerate, and finally a few lava flows. This alternation, however, is only local and shows that volcanic activity began with local extrusions.

East of the Trap Seiies (Jabal 'fiyal), the Tawilah Group is no more than 150 m thick. There, the base is a conglomerate containing fragments from the Amran Series, which demonstrates active erosion at the time of the Cretaceous transgression.

Stratigraphic observations prove that post-Jurassic tectonic movements produced undulations with a large radius of curvature. The margins of the basin were elevated, eroded, and the sedimentary debris deposited conformably on the earlier beds in the center of the

basin. Toward the margins the contact is slightly unconformable, and the basal beds of the Tawilah Group contain pebbles of the underlying Jurassic limestone.

The Tawilah Group extends slightly beyond the Trap Series to the north and east. The extent of the Tawilah Group corresponds very closely to that of the Trap Series, as if the Trap Series has protected the Tawilah from erosion.

MEDJ -ZIR SERIES

LITHOLOGY

The morphology between At 'j'awilah Kawkaban ~an'a and Wadi as Sirr is dominated by steep cliffs that are partly due to tropical erosion, which tends to form a peneplain and inselberg topography. These cliffs contain numerous caves (ancient Himyaritic tombs?) and consist of whitish-gray coarse-grained sandstone and conglomerate layers containing quartz fragments and ferruginous layers.

In the AI Gharas area, just north of Majzir, the cliffs expose Tertiary formations lithologically very similar to the underlying Cretaceous rocks.

B14 GEOLOGY OF THE ARABIAN PENINS,ULA

Section of the Medj-zir Series in cliffs just north of Majzir (Al Gharas area)

[TOtal approximate thickness of Medj-zir Series, 120m]

Trap Series at top of section. Medj-zir Series:

Sandstone with ferruginous, spherulitic concretions and nodules; appears to be a paleosol that covered the area before the extrusive phase.

Sandstone, white, mottled red, becomes finer grained and more shaly.

Sandstone, white. ·Clay, light-gray, slightly hardened. Sandstone, white. Shale, green-red, a few meters thick. Sandstone, white, fine, slightly calcareous (altered), fossil­

iferous; contains a 30-cm bed filled with worm tracks. Sandstone, white, coarse-grained, quartzitic, very compact;

contains crossbedded layers altered to a darker color (these are displayed over a great distance).

Conglomerate, 10 to 30 em thick, of rounded quartz frag­ments 1 to 3 em in diameter.

Tawilah Group sandstone at base of section.

The lowermost conglomerate layer is considered to be the base of the Medj-zir Series, and lies with apparent conformity on sandstone beds with very similar facies more than 200 m thick. At Majzir the thickness of Tertiary rocks is about 120 m. These form the upper part of the sandstone cliffs on two sides of the Rawc;l.ah plain, north of $an'a; they are also seen on the summit of Kawkaban-At '.j:'awilah (fig. 8) where the fossiliferous

Kawkoban I

layers are found in the fortress constructed on the south side of the cliff which dominates the town of At '.j:'awilah.

This series is no longer present east of the Trap Series and was not recognized in sections between At '.j:'awi:lah and Mal;twad, nor in strata exposed in horsts uplifted through the Trap Series.

The sedimentary sandy series which crops out in horizontal attitude east of the Trap Series dips under the Jabal Ash Sharafah ('.j:'iyal) massif, but the Medj-zir is not present there. On the other hand, it is apparent that the massif :U:ac;l.ur ash Shaykh, in the Ath Thillah area, is a dome and that the sedimentary series dip toward the south.

Although the age of these tectonic deformations can­not be precisely determined, the Medj-zir Series appears to be deposited in a fairly well defined basin. It is difficult to establish the direction of the transgression, but the series is apparently thicker to the west and, therefore, the sea probably came from this direction. In fact, at At '.j:'awilah, where the Medj-zir Series is no longer protected by the Trap Series, it is the same thick­ness as at Majzir town and the rocks are finer grained and more calcareous (the calcium carbonate being in large part removed by solution).

FOSSILS AND AGE

The At '.j:'awilah area has furnished only internal molds of Nerinea, as much as 7 em long, whereas

11

FrGURE 8.-Medj-zir Series above Tawilah Group in the cliffs at Kawkaban.

YEMEN B15

at the town of Majzir, northeast of E;lan'a, the fauna includes the following, which date the Medj-zir Series as Paleocene:

Myliobatus sp. Campanile, internal molds Calyptraea sp. Architectonica sp. brachiopods

The sequence at Majzir also includes slabs of ir­regular elliptical outline (from 3 to 20 em long) filled with small triangular forms grouped into hexagons that are probably due to recrystallization of calcite.

IGNEOUS ROCKS

TRAP SERIES

VOLCANIC ROCKS

The southwest part of Yemen, almost one-quarter of the country, is covered by volcanic rocks grouped into the Trap Series. The Trap Series is made up mainly of alternating lava flows, basalts, an.desite, or trachyte porphyries, and different types of varicolored tuffs (fig. 9). The maximum thickness is difficult to estimate because of faults but is locally in excess of 1,200 m.

Throughout the Trap Series are seen intrusive basaltic rocks irregularly distributed as dikes, sills, or laccoliths. The old major volcanic centers are rather rare. They are noted either by lava flows which thicken toward the centers or by the transition from tuffs to conglomerates.

Volcanic centers are also marked by chimneys standing above the general ground level. Large dikes, some of which can be followed for several kilometers, are seen in numerous places.

INTER-TRAP DEPOSITS

During the period in which the Trap Series formed there were quiet intervals, some of long duration. During these quiescent periods four types of inter-Trap deposits accumulated : 1. Fresh-water deposits, probably lacustrine, which are

fossiliferous: generally contain bituminous beds and plant and fish remains.

2. Typical alluvial deposits with fragments of partially carbonized wood.

3. Sandy deposits without fossils (fluvioeolian?). 4. Paleosol, generally lateritic, at some places developed

along plane surfaces, and locally cutting different beds.

The fossiliferous beds include small gastropods, lamellibranchs, and ostracods. These are Sphaerium sp., Amerianna sp ., Melanoides (Tarebia) cf. M. acuta (Sowerby). These fresh-water fossils, which suggest an Oligocene to Miocene age, occur from north of E;lan'a to south of Ta'izz. Mr. R. W. Morris, of the Arabian American Oil Co., recognized nonmarine ostracodes: Oandona sp., Oyprideis sp., Gomphocythere sp., and Oypridopsis ( ?) sp.

FIGURE 9.-Trap Series near Zarajah.

B16 GEOLOGY OF THE ARABIAN PENINSULA

AGE

Volcanism probably started in the south toward the end of the Cretaceous but became more intense and extensive during the Tertiary. It is characterized by extrusive and explosive periods related to tectonic deformation along faults. Volcanic activity continued into the Recent.

LACCOLITHS

GEOGRAPHIC DISTRffiUTION

The area between 'Amran and $a'dah, north of the extension of the Trap Series, has major laccolith massifs of granitic composition, some deeply breached by erosion (fig. 10). Such examples occur at Jabal Ramid south of :Uuth and in the bills near Jabal Mafluq in the Jaw£ area (fig. 11). The granitic lac­coliths are especially noticeable in the calcareous Amran Series.

In Jabal Ramid, the granite exposed in the center grades to a microgranite near the contact with lime­stone beds; the sedimentary rocks are not influenced by contact metamorphism except over a very thin interval.

AGE

Supposedly, the emplacement of the laccoliths is of the same age as the Trap Series, hence mainly Tertiary.

RECENT GRANITES

Gray-white granite hills protrude locally above the general topography carved in the Trap Series. These intrusive massifs deform the Trap Series on their flanks, and thus they are dated as post-Trap. Some intrusion reach 10 km in length and a few kilometers in width, but others may be less extensive and appear as lentic­ular dikes from 0.1 to 1.5 m wide.

Silicic granitic intrusions (leucocrats, bolocrystallines) enclose crystals of tourmaline (Jabal llufash) or amphibole (Jabal $abir, fig. 12).

RECENT VOLCANOES

Recent (Holocene) volcanoes are those which have retained their typical shape (crater or cone) and whose direction of flow has been influenced by the existing topography.

Recent volcanoes are grouped in three volcanic fields: (1) $an'a-'Amran, (2) $irwal;l-Ma'rib, and (3) Dhamar-Rada'. Isolated volcanoes are present else­where throughout the country.

In the $an'a-'Amran volcanic field it is possible to distinguish several extrusive phases by comparing the development of river terraces to the southwest of 'Amran. North of $an'a there are also volcanoes of historic time.

. . ....... . ' , · " ,, ... -.;, ... • ·~ ..!' ..... ~" · .. ~.,,·-tr·;· ~ ... ' :. • '~~· , ,"I ,;; '·. ~ .... . . . .... ' ..

FIGURE 10.-Laccolith in the Kohlan Series in the upper course of Wiidi Surdiid.

' """:;-._~Ftt ""

' t 1 ... ~. \

J~.-~tl f.: .; ··;· ;~--

.~

YEMEN

FIGURE H.-Laccoliths in Al Jawf region.

FIGURE 12.-Recent granitic massif of Jaball;labir and city of Ta'izz at base of volcanic cone.

B17

B18 GEOLOGY OF THE ARABIAN PENINSULA

Volcanoes in the $irwa.l,l-Ma'rib field are of several types. South of the $irwa.l,l-Ma'rib road are volcanoes having large cones of light-yellow tuffs surrounding the central peaks. These volcanoes have supplied thick stratified deposits of white-yellow tuff which extend for several kilometers in the direction of Wadi Adhanah. North of the road lie basaltic volcanoes with numerous adventitious craters, characterized by long flows which thin to the south.

About 3 hours walk east of $irwab. is a depression of an old crater; the tuff and agglomerate beds dip gently to the exterior and enclose blocks of gneiss and granite up to 50 em in diameter, attesting to the violence of the explosive phase.

Volcanism in Dhamar-Rada' (fig. 13) is the most recent in Yemen and the field still contains solfataras (sulfurous vents). The volcanic field is related to an east-west-trending fracture zone, along which are the main centers. Small volcanoes rise from the floor of the depression, especially in the eastern part. Seis­mic shocks are very numerous in this area.

STRUCTURE

The surface features in Yemen fit into two large very distinct categories: (1) the folded metamorphic basement of Precambrian age in unconformable contact with (2) the unmetamorphosed subhorizontal sedi-

mentary rocks. Exposures of the lower beds of the sedimentary rocks as well as the basement depend largely on erosive activity.

Orogenic movements, generally with a great radius of curvature, have locally influenced the structure of the country. For example, the area between Ash Sharafah and Ma'rib is a large dome plunging to the north.

Synclines occur particularly in the north-north of Wadi Mawr and in the 'Amasiyah area, south of $a'dah. The area covered by the Trap Series cor­responds in reality to a deep depression. The shape of the depression is most pronounced at the eastern border of the Trap Series, especially in the vicinity of Jabal 'fiyal.

Other undulations are less striking, as for example, the east-west-trending anticline at Jabal 1;£ac;l11r ash Shaykh and Jabal Mu~awwar. The $an'a area is a large syncline which extends from Wadi al Ahjar in the west to Jabal 'fiyal in the east and is the site of the old Jurassic basin.

From the fact that the coastal, or At Tihamah, part of Yemen is a graben and the eastern part a horst, it is deduced that the general structure must be dominated by subvertical faults oriented preponderantly from the north-northwest to the south-southeast, subparallel to

FIGURE 13.-Recent volcanoes near Rada.'.

YEMEN B19

the Red Sea graben and at right angles to the Gulf of Aden, which trends east-northeast-west-southwest.

Inntunerable faults, in fact, cut through the country, 1nany bounding secondary grabens and horsts. The whole zone of contact between the Red Sea plain and the Inotmtainous region is n1arked by faults trending north-northwest-south-southeast. One graben paral­lel to the Red Sea forms the main AI Jawf depression in the northeast, which is joined by a graben that fol­lows the aline1nent of the Gulf of Aden, and forms the Ramlat as Sab'atayn desert. Tectonic alinen1ents are also oblique to the former directions; this is true of the 'Amran graben and the secondary graben between I:Iarib and Ma'rib. Many secondary grabens in the area covered by the Trap Series are sometin1es difficult to distinguish fro1n the .fluviatile flat-bottomed valleys covered by thick alluvium (plains of ~an'a, Ma'bar, Yariin, AI Janndiyah, and others). However, grabens are readily distinguished in places where recent vol­canoes along the bordering faults have spread lavas toward the depressed part (Dhamar, Rada', and 'Amran grabens) (fig. 14). These grabens are characterized by a system of faults which forn1 steps along the margins and small horsts which rise in the graben floors. In 1nany places the steps look like large landslides on the sides of the horst.

Besides the system of parallel faults, there is in places a system of perpendicular faults outlining blocks which could be large horsts (north of Ta 'izz) and small isolated massifs (Jabal Kanin). The faults are easily located in the sedime~tary series where they bring heterogeneous rocks into contact (fig. 15) and thus

NW (Approx. lat 15°49'.N.; long 44°03' E.)

EXPLANATION

permit an evaluation of the throw of the fault. By contrast the faults are more difficult to study in the Trap Series.

Tectonic deformation along faults is not limited to epeirogenic movement related to the formation of the Red Sea. The fact that south of Wadi Surdud the Trap Se~!es rests directly on the Kohlan Series and that the Amran Series and Tawilah Group disappear sud­denly along the faults (fig. 16) proves that the generally east-west oriented faults locally deformed the cou.ntry long before the deposition of the Trap Series. Faults are so numerous locally that they cannot be adequately depicted on a map. The most tectonically active valley was the Wadi Surdiid, especially its upper and middle courses. Although the dip of the faults is generally steep, some have the appearance of over­thrusts (for example, between 1V1al)wad and At Tawilah where the Amran Series is thrust over the deformed Tawilah Group for a long distance).

Magma has often penetrated along faults, and the basalt has sin1ply filled up the open fissures. Secondary;· cracks cut the basalt dikes, as is evinced near ]laydan, west of Ta'izz, where the center of a basalt dike cutting Cretaceous sandstone contains a vertical bed 50 em thick composed of detrital fragments. In other places basaltic intrusions along faults have torn off large fragments of the confining rocks, as for example along the faults which outline the horsts north of Ta 'izz.

Tectonic deforn1ation possibly occurred after the emplacen1ent of the dikes. In fact, west of A~ ~afiyah (north of Ta 'izz), basalt fragments are intermingled with blocks of Cretaceous sa.ndstone (2 to 3 m wide)

s{ (Approx. lat 15°42' N.; long 44°10' E)

100 0 100 200 300 400 500 METERS Alluvium (Quaternary)

Aden Volcanic Series (Pliocene(?) and Quaternary)

Amran Series (Upper Jurassic)

FIGURE 14.-Profile of 1Amran graben. Surface of alluvium is at elevation of 2,100 m; surface of the Amran Series to the north­west is at 2,450 m.

B20 GEOLOGY OF THE ARABIAN PENINSULA

w (Approx. lat 13°47' N.; long 43°44' E.)

E (Approx.lat 13°51' N.; long 44°03' E.)

EXPLANATION 5 0 5 10 KILOMETERS

E3 L--L--L-.~--J-~--------------L-----~------~

Trap Series (Upper Cretaceous and Tertiary)

Tawilah Group (Cretaceous)

~ Amran Series (Upper Jurassic)

Basement complex (Precambrian)

FIGURE 1.5.-Schematic profile of north of Tn,'izz showing horst through Trap Series.

NE Jabal Radman (lat 15°25' N.; long 43°59' E.)

EXPLANATION

~ Trap Series

(Upper Cretaceous and Tertiary)

~ Medj-zir Series (Paleocene)

[22] Tawilah Group (Cretaceous)

1 0 1 2 3 KILOMETERS

Amran Series (Upper Jurassic)

~ Kohlan Series (Liassic)

Basement· complex (Pre cam brian )

FIGURE 16.-Structure section in· vicinity of Jabal Radman.

YEMEN B21

along rnajor faults forn1ing a thick breccia zone. .l\1any of the breccias along the faults nre restricted n.nd disappear in a short distance as n.Iong the Kaw­kaban ft1ult. The fault tntces ttre indicated by ttbrupt changes in dip; some subhori;~,ontal beds becon1e vertical near a fault contn,ct (fig. 17). Faults t;hnt can be followed for a grettt distance m·e generally cut by small right-angle fttults of 1nuch less throw u.nd later origin tlmn the 1nain fault.

" ,;) ._J ••

\ I ..J ~ V

~ ~ : ~ ~ ~ ~~. 1~: ~,!,L. J_l__l___l...__L-l-.1--_.__...._

EXPLANATION

~ Trap Series (Upper Cretaceous and Tertiary)

Tawilah Group (Cretaceous)

Amran Series (Upper Jurassic)

100 0 100 200 300 METERS

F10uru~ 17.-Prof"ile of Wadi Mnhram (lat U) 0 20' N.; Ion~ 4:3°55' E.) showing fault contacts of Tmp S<'ri<'R, Tawilnh Group, nnd Amran Seri<'R.

Southwest of .l\1abwad, not far frmn the recent granites of Jabal :S:ufash, sandstones of the Tawilah Group are bounded on two sides by faults. This is the only locality known to date where the sandstones are partially changed to quart;~,ite by dy­nttrnic or contact rnetan1orphism.

Thermn.I springs related to faults (especially along the Red Sea) explain the existence of mai)Y s1nall communities called :S:annnarn 'Ali. Hot springs are most frequently found in the 'I'rap-covered ttreas, nJthough some hot vapors are emitted fron1 caves in the limestone plateau north of :S:uth (near ·Al Barf).

Mineralization along faults is very rare and is present only in the north of the country where fttults affect the basement nnd the Jurassic limestone. Hematite deposits occur just east of Sa'dah and about 30 kn1 northwest of Sa'dah near .l\!Jajd. IJmenite deposits

are found in the Wadi Akwam basin northeast of Sa'dah.

Toward the end of the .l\1eso;~,oic, extrusion of basalt began in conjunction with the formation of the Red Sea. However, it was only from the Oligocene on that the gntben took the form of tt depressed aren. without outlet.

.l\1Iajor lava flows in association with fracturing, very active during the Oligocene and lVIiocene, extended over the southwestern part. In the same epochs the unstable zone of the Red Sea subsided in a series of secondary grabens, now filled n1ainly by salt and terrigenous deposits carried by rivers which adjusted to the new topography. At nearly the sa1ne epochs laccoliths were injected in the northern part of the country.

Deformation along faults during the Pliocene and Pleistocene played the most in1portant role in the morphology. Warping caused the formation of ~tn outlet of the Red Sea to the ocean and nccentuated the horst scarp by favoring the development of rivers and increasing headward erosion.

During the calmer and drier period of the Holocene (Recent), corals developed in the Red Sea and rivers con tinned to fill the east part of At Tiha1nah while eolian deposition predominated toward the coast.

GAZETTEER

Published sources listing Yemen place names in the original Arabic are few and incmnplete. The forms used in this work were transliterated in the systmn of the Board on Geographic Names byJ n,Jnes P . .l\1anda­ville, Jr., Arabian Affairs Division, Arabian A1nerican Oil Co. Spellings are based on written sources except those which could not be confirmed ~tnd ttre followed by a question 1nark.

The coordinates listed below refer to the mjddle courses of wadis, the highest points of n1otmtain massifs, ttnd the approximate centers of regionnl features.

Nnme Jabal 'A blah(?) ______ .. ______________ _ Wadi Adhanah ___________________ ~ __ Wadi al Ahjar_ _____________________ _ Wadi Akwam(?) ____________________ _ 'Amasiyah _________________________ _ 'Ann· an ____________________________ _ BajiL _____________________________ _ Jabal BnJaq ______________________ ---Wadi Bana ________________________ _

Jabal Barat------------------------­Al Baya~---------------------------Jabal Dakhan(?) ____________________ _ Jabal Dalhan(?) ____________________ _ Jabal J)awran ______________________ _ A~ J)ayq __________________________ _

LatN.

16°56' 15°12' 15°28' 17°02' 16°36' 15°40' 14°58' 15°30' 14°0.5' 16°47' 15°13' 15°34' 17°07' 14°45' 15° 14'

Lon(! E.

43°48' 45°07' 43°52' 43°48' 43°50' 43°56' 43°15' 45°19' 44°32' 43°52' 44°36' 45°00' 43°42' 44°11' 44°45'

B22

Name lDharnar ___________________________ _ AI Ghar as·- ________________________ _ lJajjah ____________________________ _ Sarnrnarn 'Ali ______________________ _ AI Sarf ____________________________ _ lJarib _____________________________ _ lJaydan ___________________________ _ Jabal Haylan _______________________ _ Al ij:udaydah_ -· ____________________ _ Jabal Sufash _______________________ _ ij:Qth ______________________________ _ Ibb _______________________________ _ Al J anadiyah .. ______________________ _

~~~~-j~;;f~~~~~~~~~~~~~~~~~~~~~~~~} Jabal Kanin ________________________ _ Kawkaban _________________________ _ Kharnir __________________________ _ Wadi Khawbah(?) __________________ _ Khawbat 'AlL _____________________ _ Khusran(?) ________________________ _ Kublan ____________________________ _ Wadi La'ah ______________________ _ Jabal al Lawdh _____________________ _ ~a'bar __________________________ _ Jabal ~afinq(?) ____________________ _ Wadi ~ahrarn(?) ___________________ _ ~abwad (?) _________________________ _ ~ajd(?) ___________________________ _ ~ajzir(?) __________________________ _ ~a'rib ____________________________ _ Wadi ~awr ________________________ _ ~ujabjib(?) ________________________ _ AI ~ukha _______________________ _ Jabal ~Ul;lawwar ___________________ _ Wadi Najran _______________________ _ Wadi N asirn (?) _____________________ _ Jabal an Nu'aym(?) _________________ _

Rada'------------------------------Jabal Radman ______________________ _ Wadi Raghwan(?) __________________ _ Jabal Ramid(?) _____________________ _ Ramlat as Sab'atayn ________________ _ Raw~ah ___________________________ _ Jabal $abir _______________________ .: _ $a'dah ____________________________ _ $afir ______________________________ _ A !;I $afiyah _________________________ _ A!;~ $afra' __________________________ _ $afwan ____________________________ _ $an'a ______________________________ _

Jabal ash Sharafah __________________ _ l;Ia~nr ash Shaykh __________________ _ Jabal Shu'ayb ______________________ _ As Sinnarah ________________________ _ Wadi as Sirr _______________________ _

$kwab-----------------------------Wadi Surdnd _______________________ _ Ta~zz _____________________________ _

At Tawilah _________________________ _ At Tihamah ________________________ _

Jabal TiyaL _______________________ _ A th Thillah ________________________ _

GEODOGY OF THE ARABIAN PENINSULA

LatN. Long E.

14°31' 44°28' 15°35' 44°24' 15°40' 43°34' 14°42' 44°08' 16°24' 44°11' 14°57' 45°30' 13°41' 43°45' 15°35' 45°12' 14°46' 42°57' 15°13' 43°28' 16°18' 43°55' 13°58' 44°11' 13°40' 44°10'

16°07' 44°30'

15°05' 44°30' 15°32' 43°55' 16°04' 43°58' 15°19' 43°54' 15°59' 44°01' 16°41' 43°57' 15°42' 43°42' 15°32' 43°34' 16°07' 45°07' 14°51' 44°15' 16°38' 44°11' 15°20' 43°55' 15°29' 43°32' 17°06' 43°33' 15°34' 44°36' 15°29' 45°28' 15°48' 43°18' 13°46' 43°44' 13°19' 43°14' 15°36' 43°38' 17°29' 44°08' 15°23' 43°56' 16°55' 43°30' 14°30' 44°56' 15°25' 43°59' 15°48' 45°10' 16°16' 44°07' 15°30' 45°50' 15°27' 44°13' 13°31' 44°03' 16°58' 43°45' 15°41' 46°09' 13°52' 44°03' 16°45' 43°51' 14°09' 44°35' 15°23' 44°12' 15°29' 44°42' 15°36' 43°50' 15° 19' 43°57' 16°55' 43°48' 15°33' 44°23' 15°27' 45°12' 15°21' 43°41' 13°34' 44°02' 15°30' 43°42'

-------- --------15°29' 44°42' 15°37' 43°54'

Name Wadi al 'Urr _______________________ _ Wadi W akhd (?) ____________________ _ Wadi W a '1 an _______________________ _ Y ari m _____________________________ _ Zabid _____________________________ _ Zarajah ____________________________ _

LatN.

15°17' 16°34' 15°05' 14°17' 14°10' 14°54'

SELECTED BIBLIOGRAPHY

Long E.

43°55' 44°03' 44°19' 44°26' 43°18' 44°19'

Basse, Eliane, 1930, Contribution a l'etude du Jurassique superieur (facies corallien) en Ethiopie et en Arabie meridionale: Soc. Geol. France Mem., new ser. 6, pt. 3/4, no. 14, p. 105-148.

Basse, Eliane, Karrenberg, Herbert, Lehman, J. P., Alloiteau, James, and LeFranc, J. P., 1954, Fossiles du jurassique superieur et des "gres de N ubie" de Ia region de Sanaa (Yemen): Soc. Geol. France Bull., ser. 6, v. 4, p. 655-687.

Behn, Ernst, 1910, Jernen, Grundzuge de Bodenplastic und ihr Einfiuss auf Klima und Lebewelt: Marburg, Germany.

Beneyton, M. A., 1913, Mission d'etudes au Yemen: La Geo­graphic, v. 28, no. 4, p. 201-219.

--- 1914, Railway surveys in the Yemen (with plate) Geog. Jour., v. 43, no. 1, p. 66-68.

Bent, J. T., 1900, Southern Arabia: London, Smith, Elder & Co., 455 p;

Blanckenhorn, Max, 1907, Die Hedschaz-Bahn auf Grund eigener Reisestudien: Gesell. Erdkunde, Berlin Zeitschr., p. 218-245, 288-320.

Botez, Ghorge, 1912, Rapport definitif sur le..; etudes geo­hydrologiques faites en Yemen (Arabie): Bukarest, Universala.

Botez, Ghorge, and Lange, H. G., 1925, Studii geohidrologice in Vilaetul Yemen (Schita Geologice, 1911): Inst. Geol. al Romaniei Anuarul, v. 11, p. 348.

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Brown, G. F., and Jackson, R. 0., 1959, Geologic map of the Asir quadrangle, Kingdom of Saudi Arabia: U.S. Geol. Survey Misc. Geol. Inv. Map I-217 A.

--- 1960, The Arabian Shield: Internat. Geol. Cong., 21st, Copenhagen 1960, Rept., pt. 9, p. 69-77.

Burchardt, Hermann, 1926, Aus dem Jemen (Festgabe fur den Vierten Deutschen Orientalistentag in Hamburg): Leipzig, Deutsche MorgenHi.ndische Gesellschaft, in Kommission bei F. A. Brockhaus, 7 4 p.

Burr, Frederic, 1841, Lettre sur la geologie d' Aden et sur la cote d' Arabie: Soc. Geol. France Bull., v. 12, p. 419-421.

Bury, G. W., 1911, The land of Uz, by Abdullah Mansur (G. W. Bury): London, McMillan & Co., 354 p.

Comucci, Probo, 1929, Sopra alcune rocce vulcanice della regione di Sanaa (Arabia): Soc. Toscana sci. nat.,. Mem., no. 40, p. 70-78.

--- 1933, Rocce della Iemen raccolte dalla missione de S. E. Gasparini: Periodico Mineral., v. 4, no. 1, p. 89-131.

Cox, L. R., 1929, Notes on the post-Miocene Ostreidae and Pectinidae of the Red Sea region: Malacological Soc. London, Proc., v. 18, p. 165-209.

--- 1932, Fossils, in Thomas, Bertram, Arabia Felix-Across the empty quarter of Arabia: Toronto, Jonathan Cape, app. 2, p. 364.

Dacque, Edgar, 1910, Der Jura in der Umgebung des lemurischen Kontinents: Geol. Rundschau, v. 1, p. 148-168.

Defiers, Albert, 1889, Voyage au Yemen: Paris, Paul Klincksieck, 246 p.

YEMEN B23

Fricke, Karl, H)53, Bergba.n auf Alabaster und Gips im Jemen: Gli.ickn.uf, v. 89, no. 41, p. 1061-1062.

Geukens, F. P.M., 1954, Een dn.J;!; in Yemen: Onze Alma Mater, Louvn.in, v. 3, p. 16-20.

--- 1955, Notes geologiques sur un recent voya.ge n.u Yemen: Soc. Gcol. Belgique Bull., v. 64, no. 2, p. 339-349.

---1960, Contribution ala geologie du Yemen: Inst. geol. Louvain, Mem., v. 21, p. 122-179.

Glaser, Eduard, 1913, Reise nach Marib: Wien, A. Holder, 214 p. Gumprecht, T. F., 1849, Die vulcanische Thatigkeit auf dem

Fcstlande von Afrika, in Arabien und auf den Inseln des Rothen Meers: Berlin.

J oleaud, Leonce, 1926, Sur l' origine des cassures africaines: Liege, Livre Jubilaire Soc. geol. Belgique, p. 85-88.

KmTenberg, Herbert, 1956, Junger Magma.tismus und Vulka­nismus in Si.idwesta.rabien (Jemen): Internat. Geol. Cong., 20th, Mexico City 1956, Resumenes, sec. 1, pt. 1, p. 171-185.

Lncroix, Alfred, 1900, Sur les grn.nites et syenites quartziferes a a.egyrine, arfvedsonite et aenigmatite de Madagascar: Acad. sci. [Pn.ris] Comptes re'ndus, v. 130, p. 1208-1211.

La mare, Pierre, 1923a, Note preliminaire sur la structure de ht region du Yemen: Soc. Geol. France, Sommaire des Seances~ Comptes rendus, ser. 4, v. 23, mtg. 19, p. 61.

--- 1923b, Observations geologiques sur l'Yemen: Aettd. sci. [Paris] Comptes rend us, v. 176, no. 14, p. 956-957.

--- 1923c, Sur !'existence de granites alcalins dans le Sc~am­mar (Arabie) et sur la constitution geologique de cette region: Soc. Geol. France, Comptes rend us, ser. 4, v. 23, p. 188-190.

--- 1924a, Les explorations recentes del' Arabie: La Geogra­phic, v. 41, p. 162-166.

---1924b, L'Arabie heureuse; le Yemen: La Geographic, v. 42, no. 1, p. 1-23.

--- 1925, Le volcanisme dans le Yemen: Bull .. Volcanol., no. 3/4, p. 109-112.

--- 1930a, Les manifest~ttions volcaniques post-creta.cees de la Mer Rouge and des pays limitrophes: Soc. Geol. France Mem., new ser. 6, no. 14, p. 221-223.

--- 1930b, Nature et extension des dep6ts secondaires dans 1' Arabie, l'Ethiopie et les pttys Somalis: Soc. Geol. France Mcm., new scr. 6, no. 14, p. 49-65.

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0

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